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(NoMode1.)

` M. A. HOWELL', Jr.

FILE.

l y A 'Patented Mar.6,1883.

Nrrnn `STATES MARTIN A. HOWELL, JR., OF CHICAGO, ILLINOIS.

FILE.

SPECIFICATION forming part of Letters Patent No. 273,537, dated March 6, 1883.

' Application tiled November 10I 1882. (No model.)

To all whom it may concern:

Be it known that I, MARTIN A. HOWELL, Jr., a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Files, of which the following isa specification.

The object of my invention is to produce a ile composed of metal having the essential characteristics of a true carhuret of iron, all

forging or hammering ofsaid metal being avoidc 1883. This process is essentially as follows It is well known to those skiliedin the art that no edge-tool can be cast with a cutting-edge, and owingto the peculiar hardness of the metal no cuttin g-ed ge or cuttingfteeth can be formed upon the cast blank without such expenditure of time and labor as to practically exclude the product from the market. Moreover, by all the processes in use prior to my invention for softening the metal and afterward restoring its hardness there has been no substance as yet known wherein the final product possessed the essential characteristics of a true carburet of iron. In this connection I will call attention to the fact that iron fused in contact with carbon combines with nearly six per cent. of that element. When this compound is cooled in such manner that the wholegof the carbon remains in combination with the metal the product is known as white cast-iron.77 which is extremely hard and of higher specific gravity, but brittle.

In order to convert cast-iron into bar-iron, it is necessary to remove the carbon and silicon associated with it. This is done by heatingit in contact with'oxide of iron, whereby the carbon is evolved iu the form of carbonio oxide, while the silicon, also combining with a portion of the oxide, is converted into silicic acid,

which unites with another portion, forming a fusible slag, which separates from the-metal.

In white cast-iron, however, the proportion of silicon is only about one per cent. This bariron may be again converted into cast-iron by restoring the proper percentage ot' carbon by cementation. 1n all the processes heretofore A known, however, the metal has been heated 6o in the presence ofboth carbon and oxygen, the latter being derived from the presence of atmospheric air. The consequence is that instead ofthe pure carbon with which the metal was formerly combined the known processes of cementatiou restore to the metal an oxide of carbon, and the presence of oxygen causes au oxidation of the surface of the metal, which Lin the process of converting a tool-having a cutting edge or edges or cutting-teeth from bar-iron back to white cast-iron would entirely defeat the object of my invention by reason of the brittleness of the oxide. To avoid these objections and'to produce files in finished condition and having all the characterics of a true carburet of iron, I construct said articles in the manner following: The files being first cast in molds in the form of blanks, it becomes necessary to remove the free carbon, and thereby restore the cohesion of the metal, by heating said blanks to a high degree in presence of oxygen or iu contact with an oxide. After this operation is completed the blanks are in condition to be'surfaced and cut, both which operations are performed by any of the well-l known methods. The files thus formed being now in respect of their shape, teeth, &c., practically complete, it is necessary to restore the deficiency of carbon and to combine it with vthe metal without a trace of oxide, wherebyit is 9c again converted into a true carburet ot' iron. In order to accomplish this conversion, and at the same time avoid the. oxidation of the surface by which the liles would be practically ruined, I employ the following` process: The iiles, after being decarburized and surfaced and cut in the manner already described, are

, placed in a flask orcllarger, together with substances rich in hydrocarbon, such as resins, animal and vegetable carbon, petroleum and roc its products, te. The flasks or chargers are connected by apipe with a gas-receptacle of any suitable form, and the former-viz., the askis adapted to be hermetically scaled, while the necting the two, whereby the communication between them maybe shut oil'. The exhausted gas-receptacle is placed in any suitable receptacle containing water, and weighted to keep it submerged. The ask or charger containing the files to be converted, together with the carbonaceous material, is placed in a mue or other suitable furnace, and heat applied. As the heat of the furnace advances the vapors of hydrocarbon are generated,as already mentioned, being in advance of the temperature which is necessary to saturate the metal. The

flasks containing the tiles also necessarily contain atmospheric air, and this air being mingled with the tirst vapors generated, the mixture is allowed to flow oi through any` suitable escape until the current is free from traces ot' oxygen. The outlet is then closed. and the cock in the escape-pipe is opened and the vapors allowed to flow into the exhausted vessel or gas-holder, where they are stored up for use at such a time as the advancing heat shall have raised the files to the point of saturatioirwhen the presence ot' said vapors will be required niider heavy pressure to the end ot the operation. By this tneans the vapors which under the former methods of carburization were dissipated and lost are stored up and retained for use, and all danger of an imperfect cr partial saturation is avoided,as Well as the further danger of injuring the metal by the oxidation of its surface through the presence of air. Vhen the process is complete and the liles become saturated the cock in the escape-pipe is closed, and the flask is taken froth the inue or furnace and. placed in a pit, where it is covered with dry sand, lime, clay, 0r any suitable material which will preserve the heated tlask from oxidation. Here itis allowed to cool down gradually, after which the contents are removed. The tiles being now charged with pure carbon, and no oxide being present, they will withstand a much higher heat in hardening than ordinary steel or airy partially-oxidized metal. Therefore they are hardened in the usual manner without. risk of oxidation, the result being the production of a tooth having lall the characteristics of true carbon. These tiles resist the abrasion of all ordinary metals to a degree unsurpassed by any known product of steel.

It will be noticed that some of the steps of my process are old. For example, the decarbniization ot' iron and its subsequent recarhuiization has long been known; and to this 1 lay no claim.

The special process of manufacture described above I have already disclaimed in this application as being presented in an application recently tiled by me.

The files produced in this manner hold their teeth and resist abrasion lar longer than tiles produced in any other manner. They present all the. characteristics of true carburet ot' iron, the proper percentage oi' carbon having been restored by the process ot' cementation described.

In the process of annealing cast-iron in t'ne presence of oxides or other matter having an aniry for cfirbon more or less ot' the free carbon remains in an oxidated condition. Now, by the' final process of conversion in an atmosphere ol' hydrocarbon bythe exclusion of all traces ot'oxygen the oxidated carbon is entire- I v deoxidated, leaving the metal a true carbide of iron--a standard impossible to be reached by any known process in manufacturing steel. Steel, therefore, is not a true carbide, as supposed by scientists, but an oxidated carbide of iron. ln order, therefore, to deter-lnine a true carbide from an oxidated carbide, I will explain. ln an oxidated carbide part-ot the carbon is combined with the metal. and part is crystallized between the particles of fibers. An annealing-heat will oxidize the latter by the admission of air at the point ot' expansion of the carbon, when the expansion ofthe carbo'n disintegrates the particles of metal or expands the metal, by which it becomes porous and admits air under the pressure ofthe surroundingatmosphere. 'Ihisinstantlyoxidizes it and reduces it to graphite or free carbon, which,- on breaking, after cooling gradually, is 'plainly seen in all annealed steel. When the carbon is wholly combined, as in pure white iron, or a true carburet, no process ot' annealing will show any carbon crystallized between the particles of iron; nor cati it be oxidated at a point below fusion, and in many cases until the heat is raised beyond the point of fusion. This is why pure white iroli remains pasty at or just above the melting-point. It requires an intense heat and a continuous blast to maintain tluidity, which renders thcuseofwhiteiron impractical for the foundry, and suitable only lor the forge or puddling.

Having thus described my invention, what I claim is- A carbureted cast-iron tile, substantially as IOO IIO 

